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Paratec code

Paratec is a simple DFT code optimized for small- and medium-sized systems, and with a tight integration with BerkeleyGW. Please, refer to the full documentation for PARATEC 5.1.12.

Wrapper

PARATEC output for BerkeleyGW is controlled by flags gw_shift, gwc, gwr, gwscreening, gwcscreening, and vxc_matrix_elements. The flags can be combined with an underscore: e.g. output_flags gwr_gwscreening gwr and gwc are incompatible; gwscreening and gwcscreening are incompatible.

Main flags:

  • gw_shift q1 q2 q3

    Generates q-shifted grid, q-vector is in crystal coordinates in units of reciprocal lattice vectors (for WFNq, WFNq_fi) This variable does the same job as the kgrid.x utility.

  • output_flags gwc

    Writes complex wavefunctions in G-space, for systems without inversion symmetry about the origin, to file WFN (for all codes).

  • output_flags gwr

    Writes real wavefunctions in G-space, for systems with inversion symmetry about the origin, to file WFN (for all codes)

  • output_flags gwscreening

    Writes charge density in G-space to file RHO, exchange-correlation potential in G-space to file VXC, and matrix elements of exchange-correlation potential to file vxc.dat (for Sigma). Real if possible and gwc not set, else complex.

  • output_flags gwcscreening

    Like gwscreening, except forces complex even if real is possible.

  • vxc_matrix_elements diagmin diagmax offdiagmin offdiagmax

    Specifies the range of bands for which to compute diagonal and off-diagonal matrix elements of exchange-correlation potential (for Sigma, in conjunction with output_flags gwscreening)

Other key input flags:

  • pw_job {scf, nonselfcon}

    Use scf for initial calculation, nonselfcon for generating BerkeleyGW outputs. (bandstructure does not seem to work)

  • energy_cutoff ecut

    Plane-wave cutoff for wavefunctions, in Ry.

  • number_kpoints

    • set to 0 to use k_grid and reduce with symmetries
    • set to -1 to use k_grid and do not reduce with symmetries
    • set to any other number to read from file KPOINTS

  • k_grid nx ny nz

    3 integers specifying Monkhorst-Pack k-grid dimensions

  • k_grid_shift dx dy dz

    Monkhorst-Pack k-grid shifts (typically 0.0 or 0.5)

  • number_bands nb

    Number of bands to use in calculation. Fraction actually useful or written to BerkeleyGW output determined by next variable.

  • eigspacefrac frac

    Fraction of bands to converge. Setting a higher number_bands and lower eigspacefrac can make the calculation more efficient depending on the diagonalization scheme. 0 < frac <= 1.0.

You can find the actual input files for PARATEC and BerkeleyGW in examples/DFT, in PARATEC subdirectories for each example.

There are also bgw2para and rho2cd utilities that convert BerkeleyGW files WFN and RHO to PARATEC format. This may be useful, for example, if one generates the plane waves on top of the valence and conduction bands (look into SAPO for details) and wants to diagonalize them further in PARATEC. There are no input files; bgw2para takes as argument the wfn filename, and it creates files WFN$n.$s and BAND needed for PARATEC. Similarly, rho2cd requires file RHO and it creates file CD.

Utilities

kptlist.pl

Extracts a formatted list of k-points from PARATEC file for use in the Sigma code

qptlist.pl

Extracts a formatted list of q-points from PARATEC file for use in the Epsilon code

Additional information

To build with support for BerkeleyGW output, in arch.mk set the line GWWFNPATH to BerkeleyGW/library, and add -DBGW to M4OPTLIBS.

Literature:

  • B. G. Pfrommer, J. Demmel, and H. Simon, "Unconstrained Energy Functionals for Electronic Structure Calculations," J. Comp. Phys. 150, 287 (1999).
  • B. G. Pfrommer, M. Cote, S. G. Louie, and M. L. Cohen, "Relaxation of Crystals with the Quasi-Newton Method," J. Comp. Phys. 131, 233 (1997).
  • Mathieu Taillefumier, Delphine Cabaret, Anne-Marie Flank, and Francesco Mauri, "X-ray absorption near-edge structure calculations with pseudopotentials: Application to the K-edge in diamond and alpha-quartz," Phys. Rev. B 66, 195107 (2002).
  • http://cmsn.drupalgardens.com/sites/cmsn.drupalgardens.com/files/CMSN_Newsletter_Vol2No2.pdf

The pseudopotentials for PARATEC can be generated with the fhi98PP program which is available for download at http://www.fhi-berlin.mpg.de/th/fhi98md/fhi98PP/